Molecular models of the superconducting chevrel phases: syntheses

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Inorg. Chem. 1990, 29, 764-770 Contribution from the Department of Chemistry, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan

Molecular Models of the Superconducting Chevrel Phases: Syntheses and Structures of [ M o ~ X ~ ( P Eand ~ ~[PPN][Mo,X8(PEt3),] )~] (x = s, Se; PPN = (Ph3P),N) Taro Saito,*?laNaohiro Yamamoto, Toshimi Nagase, Toshio Tsuboi, Kazuyo Kobayashi, Tsuneaki Yamagata, Hideo Imoto, and Kei Unouralb Received July 5, I989

Hexanuclear molybdenum complexes [Mo6X8(PEt3),] (1, X = S;2, X = Se) have been prepared by magnesium reduction of the reaction products of Mo3X7C14with triethylphosphine. Treatment of the complexes with sodium amalgam followed by cation exchange with (PPN)Cl (PPN = bis(triphenylphosphine)nitrogen(l+)) gave [PPN] [Mo6X8(PEt3),] (3, X = S; 4, X = Se). The X-ray structure determinations have revealed that the Mo, octahedra of the 20-electron complexes 1 and 2 are very regular in contrast to those of the solid-state compounds Mo6X8. The average bond distances are Mo-Mo = 2.663 A (l),2.704 8, (2) and Mo-X = 2.445 A (l), 2.560 A (2). The one-electron-reduced complexes 3 and 4 are slightly distorted from regular octahedra due to the occupation of the eg orbital. The average bond distances are Mo-Mo = 2.674 A (3), 2.714 8, (4) and MG-X = 2.458 (3), 2.570 8, (4). The electronic spectra of the neutral complexes indicate absorptions at 991 nm (1) and 1034 nm (2), which are assignable to a HOMO-LUMO transition. The cyclic voltammetry of 1 and 2 in T H F solutions shows a quasi-reversible one-electron-oxidation wave and two one-electron-reduction waves. The s ace group, cell constants, number of observed reflections, R, and R, are given as follows in that order. 1: Rg,a = 17.460 (3) c = 19.931 (6) A, Z = 3, 1423, 0.039, 0.043. 2: Pi, a = 13.036 (5) A, b = 20.492 (6) A, c = 12.208 (2) A, (Y = 93.31 (3)O, fl = 108.85 (l)', y = 88.85 (S)", Z = 2, 7350, 0.046, 0.041. 3: C2/c, a = 26.212 (9) A, b = 18.040 (4) A, c = 21.865 (8) A, fl = 114.87 (2)O, Z = 4, 6708,0.060, 0.079. 4: C2/c, a = 26.540 (5) A, b = 18.117 (5) A, c = 22.032 (4) A, fl = 115.39 (2)", Z = 4, 5702, 0.067, 0.045.

1,

Introduction

T h e structural chemistry of the superconducting Chevrel phases MxM06X8(M = Pb, Sn, Cu, etc.; X = S, Se, Te)* has posed the interesting problems of the relationship between the shape of the octahedral Mo, cluster and the number of electrons in the c l ~ s t e r . ~ The Mo, cluster with 24 electrons is almost regular, and as t h e number of electrons decreases from 24 to 20, the M0, octahedron becomes trigonally more elongated a n d t h e average Mo-Mo distance longer. T h e change of t h e chalcogen a t o m from sulfur to selenium also has the effect of diminishing the trigonal distortion of t h e octahedron. These tendencies were interpreted in terms of t h e net electron density in t h e metal c l ~ s t e r .However, ~ this argument was challenged by t h e different view t h a t intercluster interactions were more structure determining than the electronic e f f e ~ t .T ~ h e problem may partly be solved if t h e structures of t h e molecular cluster complexes with t h e same MosX8 (X = S, S e ) units are determined, because t h e intercluster interaction in such molecular clusters should be much smaller than in the solid-state compounds and the change of the structure would reflect major electronic effects. We have found that the reductive condensation of the trinuclear molybdenum cluster chloro-sulfido complexes leads to the formation of [Mo,S,(PE~~),].~T h e present paper describes the syntheses and structures of a selenido analogue and one-electron-reduced complexes of the sulfido and selenido complexes. The results are discussed from the viewpoint of the electronstructure relationship. Experimental Section

Reagents. Mo3X7CI4(X = S,Se) were prepared by heating MoCI, with elemental sulfur or selenium in sealed Pyrex tubes according to the (a) Present address: Department of Chemistry, Faculty of Science, The University of Tokyo, Hongo, Tokyo 1 13, Japan. (b) Department of Chemistry, Faculty of Science, Yamagata University, Yamagata 990, Japan. (2) (a) Fischer, 0., Maple, M. B., Eds. Superconductivity in Ternary Compounds I: Springer: Berlin, 1982. (b) Fischer, 0. Appl. Phys. 1978, 16, 1. (c) Chevrel, R.; Gougeon, P.; Potel, M.; Sergent, M. J. Solid State Chem. 1985.57, 25. (d) Chevrel, R.; Hirrien, M.; Sergent, M. Polyhedron 1986, 5, 87. (e) Perrin, A.; Perrin, C.; Sergent, M. J . Less-Common Mer. 1988, 137, 241. (3) (a) Yvon, K. Reference 2a, p 87. (b) Yvon, K. Current Topics in Marerials Science; Kaldis, E., Ed.; North-Holland: Amsterdam, 1979; Vol. 3, p 5 3 . (e) Yvon, K.; Paoli, A. Solid Stare Commun. 1977, 24, ( 1)

literature methods6 PEt, (Nippon Chemical Co. Ltd.) was used as received. The solvents were dried and distilled under dinitrogen. Instruments. 'H N M R spectra were measured by a JEOL FXlOO spectrometer with tetramethylsilane (internal) reference, and infrared spectra were recorded by a Hitachi 295 spectrometer (4000-250 cm-I). UV-vis spectra were obtained by Simadzu UV-265FS (300-900 nm) and Hitachi U-3400 spectrometers (900-2000 nm). XPS spectra were measured by a VG Scientific Escalab MkII instrument, and the binding energies were calibrated with C Is = 284.6 eV. Synthesis. Every operation was carried out under dinitrogen or argon. Rigorous exclusion of dioxygen was imperative to isolate the reduced cluster complexes 3 and 4. [Mo6S8(PEt3),] (1). A suspension of Mo3S7CI4(1 .O g, 1.5 mmol) in PEt, (21.6% toluene solution, 9.8 mL, 15.3 mmol) was stirred at room temperature for 24 h. The solvent and excess triethylphosphine were removed under reduced pressure, T H F (10 mL) and magnesium (74 mg, 3.1 mmol) were added to the residue, and the mixture was refluxed for 12 h. After cooling to room temperature, the solution was filtered and acetone (10 mL) was added to the filtrate, which was cooled at -20 OC. Solid product was filtered out, washed with acetone, and recrystallized from dichloromethane to give red-violet crystals; yield 32%. Anal. Calcd for C J ~ H ~ O M O ~C, P ~28.06; S ~ : H, 5.89; MO, 37.4; P, 12.1. Found: C, 28.06; H, 5.70; Mo, 38.9; P, 11.9. (Mo and P were analyzed by ICP spectrometry.) [ M O , S ~ ~ ( P E ~(2). , ) ~ ]A procedure for 1 was followed, using Mo3Se7C1, to give blue crystals; yield 21%. Anal. Calcd for C & . O M O ~ P & ~ :C, 22.56; H, 4.73; MO, 30.04. Found: C, 22.68; H, 4.69; Mo, 30.4. [PPNIMo6S8(PEt3)6] (3). Complex 1 (0.1 g, 0.07 mmol) was treated with 1% Na-Hg (1.5 g, 0.07 mmol) in T H F (10 mL) at room temperature for 15 min, and the solution was filtered into a flask containing (PPN)CI (0.04 g, 0.07 mmol). The mixture was stirred for 24 h, filtered, concentrated, and cooled at 0 OC to give deep orange crystals; yield 49%. Anal. Calcd for C72H120M06NP8S8: C, 41.58; H, 5.82; N , 0.67. Found: C, 41.92; H, 5.93; N, 0.64. [PPNIMo,Se,(PEt,),] (4). A procedure similar to that used for 3. but using 2, was followed to give deep red crystals; yield 36%. Anal. Calcd for C7,HI,,Mo,NP8Se8: C, 35.23; H, 4.93; N, 0.57. Found: C, 35.35; H, 4.83; N , 0.57. X-ray Structure Determination. Single crystals of 1, 3, and 4 were grown from a tetrahydrofuran solution and those of 2 from a dichloromethane-acetone solution, and they were sealed in glass capillaries for the X-ray measurements. The crystals of 3 and 4 contained 1 mol of tetrahydrofuran as a crystallization solvent. The space group and the approximate cell dimensions of the crystals of 1-3 were determined from oscillation and Weissenberg photographs. The crystal of 4 was found to be isomorphous with the crystal of 3 from the cell dimensions determined

41.

Corbett, J. D. J . Solid Stare Chem. 1981, 39, 56. (5) Saito, T.; Yamamoto, N.; Yamagata, T.;Imoto, H. J . A m . Chem. Soc. 1988, 110, 1646.

(4)

0020- l669/90/ 1329-0764$02.50/0

(6) (a) Opalovskii, A. A.; Fedorov, V. E.; Khaldoyanidi, K. A. Dokl. Akad. Nauk SSSR 1968,182, 1095. (b) Fedorov, V. E.: Mishchenko, A. V.; Fedin, V . P. Russ. Chem. ReL;. (Engl. Transl.) 1985, 54, 408.

0 1990 American Chemical Society

Inorganic Chemistry, Vol. 29, No, 4, 1990 765

Models of the Superconducting Chevrel Phases Table 1. Crystal Parameters and X-ray Diffraction Data for 1-4 1

2

3

formula

Cd%oM06P6S8

fw

1541.12 R3 17.460 (3)

C36HmM06P6Se8 1916.27 Pi 13.036 (5) 20.492 (6) 12.208 (2) 93.31 (3) 108.85 I l l 88.85 (5)' 3081 (2) 2 60.2 1.OO-1.48 7350, (>6a) 0.041, 0.046

C76H I 28M06NP8S8 21 51.82 C2fc 26.212 (9) 18.040 (4) 21.865 (8)

CXHI~~MO~NPSS~B 2526.91

114.87 (2) .,

115.39 (2)

9380 (6) 4 11.0

9570 (4) 4 39.28 1.00-1.62 5702, (>60) 0.066, 0.043

space group

A b, A c, A

a,

19.931 (6)

deg & deg Y* deg CY,

v, A'

5262 (2) 3 14.02 1 .oo-1.23 1423, (>60) 0.039, 0.043

Z

cm-' abs cor" obsd reflcnsb R, RwC

p,

4

1.00-1.1 1

6708, (>6a) 0.058, 0.079

a / c

26.540 ( 5 ) 18.117 (5) 22.032 (4)

" Relative absorotion correction coefficient (emoirical . . &scan method). bNumber of observed reflections with the criterion for the observations in parentheses. w 1 /a2(F,,). Table 11. Fractional Atomic Coordinates and Equivalent Isotropic Thermal Parameters' for IMoSdPEt,Ll f 1) X

0.03505 (6) 0.0000 -0.1 I94 (2) 0.0877 (2) 0.1622 (7) 0.1958 (9) 0.1491 (8) 0.2354 (8) -0.0002 (8) -0.0542 (8)

Y 0.10021 (5)

0.0000 0.0638 (2) 0.2375 (2) 0.2441 (7) 0.3291 (9) 0.3436 (6) 0.3571 (7) 0.2503 (8) 0.1819 (IO)

z

0.05450 (4) 0.1499 (2) 0.0504 ( I ) 0.1254 ( I ) 0.1954 (5) 0.2394 (6) 0.0802 (6) 0.0487 (6) 0.1662 (6) 0.2181 (6)

u,,

z

0.0234 (3) 0.034 ( I ) 0.031 ( 1 ) 0.036 ( I ) 0.051 (5) 0.083 (8) 0.050 (5) 0.064 (6) 0.057 (6) 0.068 (7)

"The isotropic equivalent thermal parameters are defined as Uw = (1 /3)~i~u~i*~j*(ai.ai).

by a diffractometer and intensities of the low-angle reflections. X-ray measurements of the crystals were performed at 20 "C on a Rigaku AFC-4 diffractometer equipped with a Rotaflex rotating anode X-ray generator (the crystals of 1-3) or a Rigaku AFC-6 diffractometer with a sealed normal-focus X-ray tube (the crystal of 4). The radiation used was Mo Ka monochromatized with graphite (0.71069 A). The intensity data of all crystals did not indicate any decay, and data were corrected for the Lp factor and empirically for the absorption. The positions of the heavy atoms (molybdenum, chalcogen, and phosphorus atoms) of 1-3 were determined by direct methods using MULTAN~S. As the starting positional parameters of 4,the same coordinates of the heavy atoms as found in 3 were used. The carbon and nitrogen atoms were located on the Fourier maps, and all non-hydrogen atoms were refined by the full-matrix least-squares method. In the last stage of the refinement of 1, hydrogen atoms were included at calculated fixed positions. Hydrogen atoms were not included in the calculations of 2-4. The tetrahydrofuran in the crystals of 3 and 4 was distributed in two neighboring positions, which were related to each other by inversion symmetry. Since its oxygen atom could not be distinguished from the carbon atoms, the tetrahydrofuran molecule was treated as a C5 ring. In the refinement of 3, the positions of the atoms of tetrahydrofuran were located at the fixed positions found on the Fourier map. In the case of 4, the atomic positions of the tetrahydrofuran molecule were determined from the Fourier map so that it had the shape of a planar pentagon with the C-C distance of 1.50 A. The comparison of the observed and calculated structure factors of the strong reflections of 4 showed an obvious effect of extinction, and the extinction parameter y was introduced in the refinement of 4 as IFc(cor)l = lFc(raw)l/( I + yLplFc(raw)12)1/2. The crystallographic data are given in Table I, and other details, in the supplementary material. The final atomic parameters of 1-4 are listed in Tables 11-V. Electrochemistry. Voltammetry was performed on a HECS-3 12B polarographic analyzer with a HECS-321 B function generator (Huso Co.). A three-electrode cell consisting of a glassy-carbon-disk working electrode (diameter 0.3 cm), a Pt-coil auxiliary electrode, and a saturated sodium calomel reference electrode (NaSCE) was used for the measurements. The ferrocenefferrocenium (Fc/Fc+) redox couple was used as a standard of potential. Thin-layer coulometry was carried out on a HECS-312B polarographic analyzer coupled with a HECS-978 coulometer (Huso Co.) by

Figure 1. ORTEP drawing of [ M ~ ~ f i e , ( P E t (2A). ~ ) ~ ] ,411 hydrogen atoms are omitted for clarity.

using a micrometer thin-layer electrochemical cell with a glassy-carbon disk (diameter 0.3 cm) as a working electrode.' Tetrabutylammonium tetrafluoroborate (Nakarai Tesque Inc., specially prepared reagent for polarography) was used as the supporting electrolyte without further purification. Reagent grade dichloromethane (Wako Pure Chemicals Industries) was refluxed over CaH, for several hours and then was fractionally distilled. Reagent grade tetrahydrofuran (Wako Pure Chemicals Industries) was refluxed over CuCl for 30 min and then purified by fractional distillation.

Results Synthesis. As described in our previous c o m m ~ n i c a t i o nthe ,~ hexanuclear molybdenum complex 1 was initially prepared from an isolated trinuclear cluster complex coordinated with both triethylphosphine and methanol. We found subsequently t h a t 1 was more conveniently prepared directly by t h e reduction with magnesium of the reaction product of Mo3S7CI4with triethylphosphine (eq 1). T h e selenido analogue 2 was also prepared

M03X7C14 + 8PEt3

-

" [ M o ~ X ~ C I ~ ( P E+~ ~ 3XPEt3 )~]"

+ 4Mg [Mo,X,(PEt3),j]

2"[Mo3X4C14(PEt,)~ln

+ 4MgC12 + 4PEt3 (1)

by the similar procedure. Both 1 and 2 a r e rather stable toward air, b u t t h e reduced clusters 3 a n d 4 a r e extremely sensitive t o air oxidation and return to the neutral cluster complexes readily. Therefore, t h e reductions with sodium amalgam followed by t h e cation exchange by PPN salt were carried out under argon with utmost care to exclude trace oxygen. (7) Hubbard, A. T.; Anson, F. C. Electroanalytical Chemistry; Bard, A.J., Ed.; Marcel Dekker: New York, 1970; Vol. 4, p 129.

766 Inorganic Chemistry, Vol. 29, No. 4, 1990

Saito et ai.

Table 111. Fractional Atomic Coordinates and Equivalent Isotropic Thermal Parameters' for atom X Mo(l) -0.09696 (8) M O ( ~ ) 0.08746 i 8 j Mo(3) -0.08371 (8) Se(l) 0.09549 (IO) Se(2) 0.25336 (9) Se(3) -0.08737 (IO) Se(4) 0.06971 (IO) P(l) -0.2299 (3) P(2) 0.2068 (3) P(3) -0.1935 (3) Mo( I b) 0.39883 (8) Mo(2b) 0.57071 (8) Mo(3b) 0.40688 (8) Se(3b) 0.55975 (IO) Se(4b) 0.24892 (IO) Se( I b) 0.42544 ( I O ) Se(2b) 0.38241 (IO) P( I b) 0.2649 (3) P(2b) 0.6654 (3) P(3b) 0.2831 (3) C(11) -0.298 ( I ) C(I1) -0.298 ( I ) C(12) -0.368 ( I ) C( 13) -0.346 ( I ) C( 14) -0.426 ( I ) C(15) -0.173 ( I ) C(16) -0.130 ( I ) C(21) 0.139 ( I ) C(22) 0.078 ( I ) C(23) 0.310 ( I ) C(24) 0.388 ( I ) C(25) 0.282 ( I ) C(26) 0.371 ( I ) C(31) -0.341 ( I ) C(32) -0.361 ( I ) C(33) -0.140 ( I ) C(33) -0.140 ( I ) C(34) -0.204 (2) C(35) -0.210 ( 1 ) C(36) -0.097 ( 1 ) C(lIb) 0.146 ( I ) C( 12b) 0.067 ( I ) C(13b) 0.203 ( I ) C(14b) 0.134 ( I ) C(15b) 0.321 ( I ) C(16b) 0.359 ( I ) C(21b) 0.580 ( I ) C(22b) 0.537 ( I ) C(23b) 0.778 ( I ) C(24b) 0.841 (2) C(25b) 0.720 ( I ) C(26b) 0.813 (2) C(31b) 0.193 (1) C(32b) 0.109 ( I ) C(33b) 0.190 ( I ) C(34b) 0.1 13 (2) C(35b) 0.350 ( 1 ) C(36b) 0.417 ( I )

IMorSea(PEt2Ll (2) Y Z 0.01051 (4) 0.08857 (8) 0.06965 i4j 0.09178 i8j 0.06128 (4) -0,10576 (8) 0.11431 (5) -0.09717 (IO) -0.00187 ( 5 ) 0.10203 (IO) 0.13432 (5) 0.06999 ( I O ) 0.01790 (5) 0.27035 (IO) 0.2018 (3) 0.0233 (2) 0.1584 ( I ) 0.2220 (3) -0.2502 (3) 0.1418 ( I ) 0.49047 (4) 0.08182 (9) 0.56869 (4) 0.10927 (9) 0.56266 (4) -0.09375 (9) 0.49628 (6) 0.26942 (IO) 0.48555 (6) -0.1 1519 (1 1) 0.06214 ( 1 1 ) 0.36654 (5) 0.61523 (5) 0.09214 ( 1 1 ) 0.4799 (2) 0.1922 (3) 0.6617 (2) 0.2499 (3) -0.2253 (3) 0.6436 (2) 0.6436 (2) -0.2253 (3) 0.104 ( I ) 0.199 ( I ) 0.122 ( I ) 0.077 ( I ) -0.034 ( I ) 0.152 ( I ) -0.029 (1 ) 0.226 ( 1 ) 0.015 ( I ) 0.361 ( I ) -0.055 ( I ) 0.392 ( I ) 0.224 ( 1 ) 0.284 ( 1 ) 0.198 ( I ) 0.365 ( I ) 0.126 ( I ) 0.349 ( I ) 0.178 ( I ) 0.434 ( I ) 0.211 ( I ) 0.155 ( I ) 0.173 ( I ) 0.119 ( I ) -0.319 ( I ) 0.125 ( I ) 0.061 ( I ) -0.401 ( 1 ) 0.061 ( I ) -0.401 ( I ) -0.372 ( I ) 0.149 ( I ) 0.196 ( I ) -0.466 (2) -0.197 ( I ) 0.226 ( I ) -0.156 ( I ) 0.263 ( I ) 0.535 ( I ) 0.149 ( I ) 0.221 ( 1 ) 0.533 ( I ) 0.184 ( I ) 0.398 ( I ) 0.375 ( I ) 0.060 ( I ) 0.354 ( I ) 0.492 ( I ) 0.391 (1) 0.565 ( I ) 0.734 ( I ) 0.263 ( I ) 0.771 ( 1 ) 0.153 (2) 0.215 ( I ) 0.697 ( I ) 0.754 ( I ) 0.300 (2) 0.405 ( I ) 0.645 ( I ) 0.592 ( I ) 0.427 (2) -0.167 (1) 0.696 ( 1 ) -0.137 ( I ) 0.658 ( 1 ) -0.360 ( I ) 0.604 ( I ) 0.649 ( I ) -0.444 (2) -0.273 ( 1 ) 0.711 ( I ) -0.352 ( I ) 0.686 ( I )

uq,A2 0.0231 (3) 0.0223 i3j 0.0229 (3) 0.0325 (4) 0.0306 (4) 0.0323 (4) 0.0306 (4) 0.037 ( I ) 0.034 ( 1 ) 0.038 ( I ) 0.0268 (3) 0.0276 (4) 0.0268 (3) 0.0355 (4) 0.0363 (5) 0.0349 (4) 0.0378 (5) 0.040 ( I ) 0.048 ( I ) 0.040 (1) 0.040 ( I ) 0.054 (4) 0.060 (4) 0.054 (4) 0.075 (5) 0.048 (3) 0.066 (4) 0.045 (3) 0.058 (4) 0.052 (3) 0.078 (5) 0.050 (3) 0.068 (4) 0.058 (4) 0.071 (4) 0.071 (4) 0.055 (4) 0.097 (6) 0.059 (4) 0.079 (5) 0.057 (4) 0.078 (5) 0.055 (4) 0.063 (4) 0.064 (4) 0.078 (5) 0.069 (4) 0.083 (5) 0.068 (4) 0.099 (6) 0.073 (5) 0.096 (6) 0.057 (4) 0.072 (4) 0.059 (4) 0.090 (6) 0.052 (3) 0.069 (4)

Osee the footnote a of Table 11. Structure. The structure of complex 1 has been comm~nicated,~ but the detailed structural data are given for the purpose of comparison with the other cluster compounds in Tables I1 and V I . Complex 2 crystallizes in the triclinic space group Pi,and there are two independent molecules, 2A and 2B, in a unit cell. The selected interatomic distances and angles are listed in Table V11. Figure 1 illustrates the structure of 2A, which is virtually identical with that of 2B. The average Mo-Mo bond distance for 2 is longer than that for 1 by 0.041 (1) A; namely the selenido cluster is a little larger than the sulfido cluster. Just like that of the sulfido analogue 1, the structure of 2 is characterized by its regular octahedral framework of six molybdenum atoms that bond to each other with the Mo-Mo bond distances ranging from 2.697 ( I ) to 2.708 ( I ) A. The Mo-Mo-Mo

/

Figure 2. ORTEP drawing of the unit cell of [PPN][Mo,Se,(PEt,),] projected on the ac plane.

(3)

OlC,

Figure 3.

ORTEP

drawing of 3, showing a [Mo,S,(PEt,)J

ion

bond angles also exhibit its regular octahedral structure. There is no indication that the structures of 1 and 2 are trigonally distorted like the solid-state compounds Mosss and Mosses, whose clusters are trigonally elongated! or like the 20-electron niobium clusters in Nb6111H9 and CsNb6111,10 which are trigonally twisted. In 1 and 2, it is very improbable that orientational disorder of trigonally distorted clusters leads to the seemingly regular shape because such trigonal distortions are likely to be frozen in the structure of 1, where the cluster is located on the crystallographic 3-fold axis. One-electron reduction of 1 formed 3, which crystallized in the monoclinic space group C2/c. The selected interatomic distances and angles are listed in Table VIII. The unit cell structure is illustrated in Figure 2, and the molecular structure, in Figure 3. The average Mo-Mo bond distance 2.674 (1) 8, is a little (0.01 1 (1) A) longer than that of the neutral cluster 1. The Mo-r3-S bond distances for 2 are also 0.01 3 (2) A longer than those for 1.

The selenido analogue 4 crystallizes in the monoclinic space group C2/c and is isomorphous with 3. The selected interatomic distances and angles are listed in Table IX. There is some disorder of tetrahydrofuran and of the ethyl groups of the triethylphosphine ligands. The overall structure is slightly distorted, and the average Mo-Mo and Mo-Se bond distances are longer than those for 2. (8) Bars, 0.;Guiflevic,J.; Grandjean, D. J . Solid State Chem. 1973,6,48. (9) Imoto, H.; Simon, A. Inorg. Chem. 1982, 21, 308. (IO) Imoto, H.: Corbett, J. D. Inorg. Chem. 1980, 19, 1241.

Inorganic Chemistry, Vol. 29, No. 4, 1990 167

Models of the Superconducting Chevrel Phases Table IV. Fractional Atomic Coordinates and (Equivalent) Isotropic Thermal Parameters' for [PPN][Mo&(PE~,)~].THF(3) atom X Y Z Um/ilor A2 0.71252 (3) 0.80252 (3) 0.79606 (4) 0.7088 ( I ) 0.72109 (1 1) 0.6247 ( I ) 0.80637 ( 1 1) 0.6639 ( I ) 0.8696 ( I ) 0.8588 ( I ) 0.04225 (12) 0.0000 0.6140 (6) 0.5843 (6) 0.7141 (6) 0.7400 (6) 0.6237 (5) 0.5725 (6) 0.8853 (6) 0.8330 (6) 0.8458 (6) 0.889 ( I ) 0.9546 (7) 0.955 ( 1 ) 0.9138 (7) 0.953 ( I ) 0.903 ( 1 ) 0.855 ( I ) C(17) 0.825 ( I ) C(181)b 0.817 (2) C(182)b 0.785 (2) C(19) 0.0647 (4) C(20) 0.0378 (4) C(21) 0.0548 (5) C(22) 0.0954 (6) C(23) 0.1218 (6) C(24) 0.1062 (5) C(25) 0.0111 (4) C(26) 0.0481 (5) C(27) 0.0237 (6) C(28) -0.0335 (7) C(29) -0.0689 (6) C(30) -0.0459 (5) C(31) 0.1039 (4) C(32) 0.0976 (5) C(33) 0.1473 (6) C(34) 0.1952 (6) C(35) 0.2007 (7) C(36) 0.1533 (6) C(37)? 0.2944 C(38)' 0.2722 C(39)' 0.2444 C(40)c 0.2222 C(41)? 0.2056

0.33266 (4) 0.51454 (4) 0.48869 (4) 0.31433 (5) 0.59324 (4) 0.24487 (5) 0.6090 (1) 0.2630 ( I ) 0.38943 (14) 0.41709 (13) 0.2716 ( I ) 0.4384 ( I ) 0.37951 (14) 0.58850 (13) 0.5349 (2) 0.4466 (2) 0.4800 (2) 0.4122 (2) 0.7185 ( I ) 0.2348 (2) 0.22643 (14) 0.22119 (14) 0.1980 (6) 0.2500 0.4265 (8) 0.5734 (7) 0.4933 (9) 0.5894 (8) 0.5220 (8) 0.5906 (7) 0.4911 (9) 0.6640 (8) 0.4620 (7) 0.5086 (8) 0.4088 (7) 0.4698 (8) 0.4147 (8) 0.4047 (7) 0.3410 (8) 0.4214 (8) 0.4888 (7) 0.5064 (8) 0.570 ( I ) 0.489 ( I ) 0.4008 (IO) 0.5504 (9) 0.606 (2) 0.403 (2) 0.7349 (8) 0.1643 (9) 0.147 ( I ) 0.805 ( I ) 0.320 ( I ) 0.763 (1) 0.365 (2) 0.779 ( I ) 0.782 (2) 0.213 (2) 0.766 (2) 0.153 (2) 0.778 (2) 0.179 (3) 0.2443 (5) 0.3204 (6) 0.1983 (6) 0.3774 (6) 0.2222 (7) 0.4529 (7) 0.2844 (8) 0.4648 (8) 0.3278 (8) 0.4085 (9) 0.3087 (6) 0.3326 (7) 0.1296 (5) 0.2197 (6) 0.0982 (6) 0.2302 (7) 0.0266 (7) 0.2256 (8) -0.0062 (8) 0.2153 (9) 0.0246 (8) 0.2077 (8) 0.0970 (7) 0.2086 (7) 0.2546 (5) 0.1672 (6) 0.2799 (6) 0.1001 (7) 0.3053 (7) 0.0509 (8) 0.3014 (8) 0.0743 (9) 0.2737 (8) 0.1413 (9) 0.2482 (7) 0.1910 (8) 0.5000 0.2500 0.4643 0.2333 0.4429 0.2250 0.4571 0.21 33 0.4786 0.2250

0.0380 (3) 0.0396 (3) 0.0395 (3) 0.049 ( I ) 0.0474 (1 1) 0.048 ( I ) 0.0485 (1 1) 0.053 ( I ) 0.069 (2) 0.067 ( I ) 0.0484 (12) 0.055 (3) 0.090 (4) 0.113 (5) 0.093 (4) 0.114 (5) 0.086 (4) 0.100 (5) 0.094 (4) 0.104 (5) 0.101 (5) 0.163 (8) 0.132 (6) 0.110 (IO) 0.1 18 (6) 0.203 (1 0) 0.158 (8) 0.092 (9) 0.252 (1 5) 0.112 (11) 0.150 (16) 0.054 (3) 0.063 (3) 0.079 (4) 0.094 (4) 0.105 (5) 0.077 (4) 0.054 (3) 0.075 (4) 0.093 (4) 0.105 (5) 0.105 (5) 0.081 (4) 0.059 (3) 0.070 (3) 0.093 (4) 0.103 (5) 0.1 10 (5) 0.089 (4) 0.19 0.19 0.19 0.19 0.19

"The molybdenum, sulfur, and phosphorus atoms were refined anisotropically. See footnote a of Table 11. b A methyl carbon atom occupies two sites, C(181) and C(182). The occupancy factors of these sites were fixed as 0.5. ?These atoms were of the disordered THF molecule and were not refined.

Table V. Fractional Atomic Coordinates and (Equivalent) Isotropic Thermal Parameters" for lPPN1IMo6Sen(PEtMTHF(4) atom X Y z UWh,A2 Mo(I) 0.71269 16) 0.33347 (IO) 0.51523 (8) 0.0366 (IO) 0.80232 (6j 0.79724 (6) 0.70944 (7) 0.71919 (7) 0.62018 (7) 0.80954 (7) 0.6633 (2) 0.8681 (2) 0.8616 (2) 0.5406 (2) 0.5000 0.6100 (7) 0.5824 (7) 0.707 (1) 0.734 (1) 0.6260 (7) 0.5752 (7) 0.884 ( I ) 0.8319 (7) 0.846 (1) 0.886 ( I ) 0.948 ( I ) 0.955 ( I ) 0.920 ( I ) 0.953 ( I ) 0.905 (1) 0.854 ( I ) 0.956 (2) 0.831 ( I ) 0.804 ( I ) 0.5106 (6) 0.5451 (7) 0.517 ( I ) 0.460 ( I ) 0.425 ( I ) 0.453 ( I ) 0.5624 (6) 0.6067 (7) 0.619 ( I ) 0.590 (1) 0.548 ( I ) 0.5349 (6) 0.6017 (7) 0.6526 (7) 0.701 ( I ) 0.694 ( I ) 0.6442 (8) 0.5947 (7) 0.2500 0.2049 0.2221 0.2779 0.2951

0.31485 ( i o j 0.24465 (IO) 0.26350 (12) 0.39516 (11) 0.27306 (11) 0.38474 (12) 0.4462 (3) 0.4132 (3) 0.2344 (4) 0.2709 (3) 0.2975 (IO) 0.4230 (11) 0.4910 (12) 0.520 (1) 0.491 ( I ) 0.5102 (11) 0.4728 (IO) 0.414 ( I ) 0.4289 (11) 0.511 (1) 0.564 (2) 0.403 (2) 0.414 (2) 0.160 ( I ) 0.142 (2) 0.319 (1) 0.367 (2) 0.337 (2) 0.216 (2) 0.165 (2) 0.2785 (9) 0.2731 (12) 0.274 ( I ) 0.285 ( I ) 0.292 ( I ) 0.289 ( I ) 0.1752 (IO) 0.1567 (12) 0.080 ( I ) 0.030 ( I ) 0.044 ( I ) 0.1181 (11) 0.3300 (11) 0.3038 (IO) 0.357 ( I ) 0.423 ( I ) 0.4459 (1 1) 0.4026 (1 1) 0.3202 0.2717 0.1932 0.1932 0.2717

0.48804 (8j 0.59431 (7) 0.61436 (8) 0.41361 (9) 0.43668 (9) 0.59251 (IO) 0.5354 (3) 0.4775 (3) 0.7198 (2) 0.7197 (2) 0.7500 0.5689 (9) 0.5825 (9) 0.590 (1) 0.666 ( I ) 0.4653 (9) 0.4078 (9) 0.403 ( I ) 0.3409 (9) 0.486 ( I ) 0.480 (1) 0.531 (2) 0.590 (2) 0.739 ( I ) 0.806 ( I ) 0.763 ( I ) 0.778 (2) 0.731 (2) 0.779 ( I ) 0.776 (2) 0.6317 (7) 0.5972 (9) 0.526 ( I ) 0.489 ( I ) 0.525 ( I ) 0.598 ( I ) 0.7401 (9) 0.8061 (9) 0.822 ( I ) 0.777 ( I ) 0.715 ( I ) 0.6939 (8) 0.7523 (8) 0.7460 (8) 0.774 ( I ) 0.798 (1) 0.8008 (9) 0.7753 (9) 0.5000 0.45 17 0.4701 0.5299 0.5483

0.0375 (ioj 0.0377 (IO) 0.0444 (1 1) 0.0430 (1 2) 0.0456 (1 1) 0.0455 (12) 0.048 (3) 0.062 (4) 0.061 (3) 0.047 (3) 0.044 (6) 0.063 (6) 0.085 (7) 0.090 (7) 0.089 (7) 0.063 (6) 0.057 (6) 0.079 (7) 0.067 (6) 0.073 (7) 0.149 (11) 0.163 (12) 0.207 ( I 5) 0.084 (7) 0.151 (11) 0.131 (10) 0.052 (1 1) 0.101 (16) 0.161 (13) 0.215 (17) 0.041 (5) 0.081 (7) 0.099 (8) 0.097 (8) 0.092 (8) 0.084 (7) 0.043 (5) 0.066 (6) 0.085 (8) 0.076 (7) 0.078 (7) 0.048 (5) 0.052 (5) 0.064 (6) 0.091 (8) 0.087 (7) 0.080 (7) 0.062 (6) 0.323 0.323 0.323 0.323 0.323

The molybdenum, selenium, and phosphorus atoms were refined anisotropically. b A methyl carbon atom occupies two sites, C(181) and C(182). The occupancy factors of these sites were fixed as 0.5. eThese atoms were of the disordered THF molecule and were not refined. Table VI. Interatomic Distances (A) and Angles (deg) for [Mo&(PEt&,l (1)o

The pertinent bond distances of the relevant cluster compounds are listed in Table X . Spectra. (a) Electronic Spectra. The cluster complexes exhibit characteristic absorptions in the visible and near-infrared regions. The peak positions and intensities are given in Table XI. The lower energy bands have shoulders, and the higher energy bands are split in the case of the selenido derivatives. (b) XPS. The peak positions in the X-ray photoelectron spectra of the complexes 1 and 2 are shown in Table XI. The valence band spectra will be discussed elsewhere in relation to the X a calculation of a model system.']

y.

( I I ) Imoto, H.; Adachi, H.; Saito, T. To be published.

Electrochemistry. The cyclic voltammograms of the cluster complexes 1 and 2 were measured in dichloromethane and THF

M~-MO" Mo-Mo" Mo-S(Z) Moiii-S(2)

3.766 (1) 2.662 (1) 2.444 (3) 2.439 (3)

MO"'-MO"O'' Moi'-Mo-S(2) Mo-S(2)-Moiii

59.98 (3) 117.14 (8) 66.13 (8)

" Equivalent positions: -2;

(v) -x

+ y , -x,

Mo-Moiii Mo-S(I) Mo-P MoV'-S(2)

2.664 ( I ) 2.446 (2) 2.527 (3) 2.449 (3)

Moii'-M~MoiV 90.0 M o V ' - M ~ S ( 2 ) 57.15 (7) 135.38 (8) MoVi-Mo-P

(ii) -x, -y, -2; (iii) -y, x z ; (vi) x - y, x, -2.

- y , z;

(iv) y , -x

+

768 Inorganic Chemistry, Vol. 29, No. 4, 1990 Table VII. Interatomic Distances [MO6Ses(PEtj)61 ( 2 4 28)‘ Mo(l)-Mo(l)’ 3.825 (1) Mo( ~)-Mo(2)’ 3.820 ( I ) M0(3)-M0(3)’ 3.824 ( I ) Mo( l)-M0(2) 2.702 ( I ) Mo( 1)-M0(3) 2.701 ( I ) Mo( l)-M0(2)’ 2.704 ( I ) Mo(l)-MO(3)’ 2.708 ( I ) MO( 2)-MO(3) 2.705 ( I ) MO(Z)-Mo( 3)’ 2.701 ( I ) Mo( 1)-Se( 3) 2.570 (2) Mo( I)-Se(4) 2.555 (2) Mo( I)-%( I)‘ 2.566 (2) Mo( l)-Se(2)’ 2.550 (2) Mo(2)-Se( I ) 2.564 (2) Mo( 2)-Se( 2) 2.561 (2) Mo(2)-Se(3) 2.559 (2) 2.556 (2) Mo(2)-Se(4) 2.565 (2) Mo(3)-Se( I ) Mo(3)-Se( 3) 2.557 (2) Mo( 3)-Se(2)’ 2.560 (2) Mo( 3)-Se(4)’ 2.560 (2) Mo( 1)-P( I ) 2.544 (3) M0(2)-P(2) 2.538 (3) Mo(3)-P( 3) 2.548 (3)

Mo(~)-Mo(l)-Mo(3) MO(3)-MO( I )-Mo(3)’ Mo( I )-Mo( 2)-Se( 1 )1 Mo(3)-Mo(Z)-Se( I )I Mo(2)-Se( 1 )-Mo(3) I Mo(~)-Mo(I)-P( 1)

Saito et al.

(A) and Angles (deg) for Mo(lb)-Mo(lb)’ Mo(2b)-M0( 2bj’ Mo( 3b)-Mo(3 b)’ Mo( I b)-M0(2b) Mo( 1b)-M0(3b) Mo(l b)-M0(2b)’ Mo( 1b)-M0(3b)’ Mo( 2b)-M0( 3b) Mo( 2b)-M0( 3b)’ Mo( 1b)-Se(3b) Mo( 1b)-Se(4b) Mo( 1b)-Se( 1b) Mo( 1b)-Se(2b) Mo(2b)-Se( 1b)’ Mo( 2b)-Se(2b) Mo(2b)-Se(3b) Mo(2b)-Se(4b)’ Mo(3b)-Se( 1b)‘ Mo( 3b)-Se( 3b)’ Mo( 3b)-Se( 2b) Mo(3b)-Se(4b) Mo( 1b)-P( 1b) Mo(2b)-P( 2b) Mo(3b)-P( 3b)

1 + 10

3.826 (1) 3.821 ( i j 3.817 (1) 2.702 ( I ) 2.704 (1) 2.706 ( I ) 2.700 (1) 2.697 ( I ) 2.704 ( I ) 2.556 (2) 2.561 (2) 2.564 (2) 2.561 (2) 2.556 (2) 2.565 (2) 2.563 (2) 2.562 (2) 2.559 (2) 2.555 (2) 2.566 (2) 2.558 (2) 2.546 (4) 2.541 (4) 2.543 (4)

1

1.0

89.86 (4) 58.02 (4) 118.11 ( 5 ) 63.64 (4) 134.04 (9) -2.

Table VIII. Interatomic Distances (A) and Angles (deg) for IPPNI[Mo6Ss(PEtd61 (3)’ Mo(l)-Mo(l)’ 3.770 ( I ) Mo(2)-M0(2)’ 3.789 ( I ) M0(3)-M0(3)’ 3.770 ( I ) Mo(l)-M0(2) 2.668 (1) Mo(l)-M0(3) 2.664 (1) Mo(l)-M0(2)’ 2.677 (1) Mo(l)-M0(3)’ 2.667 ( I ) M0(2)-M0(3) 2.674 ( I ) M0(2)-M0(3)’ 2.671 (1) Mo(l)-S(I) 2.454 (3) Mo( I)-S(2) 2.458 (3) Mo(l)-S(3) 2.462 (3) Mo(I)-S(4) 2.457 (3) M0(2)-S(l)’ 2.462 (3) M0(2)4(2) 2.456 (3) Mo(2)-S(3)’ 2.454 (3) Mo(2)-S(4) 2.444 (3) Mo(3)-S(I) 2.473 (3) Mo(3)-S(2)’ 2.457 (3) Mo())-S(3)’ 2.468 (3) Mo(3)-S(4) 2.451 (3) Mo(l)-P(I) 2.554 (3) M0(2)-P(2) 2.556 (4) Mo(3)-P(3) 2.540 (4)

Mo(2)-Mo(l)-M0(3) M0(2)-Mo(l)-S(l) Mo(l)-S(l)-M0(2)’

60.21 (3) 117.78 (7) 66.01 (8)

Mo(3)-Mo(l)-M0(3)‘ Mo(Z)’-Mo(l)-S(I) Mo(Z)-Mo(l)-P(I)

+ It2,

+

-2.

Table I X . Interatomic Distances (A) and Angles (deg) for [PPNI [Mo6Ses(PEt&.] (4) Mo(l)-Mo(l)’ 3.837 (3) Mo(2)-M0(2)’ M0(3)-M0(3)’ 3.829 (2) Mo(l)-M0(2) Mo(l)-M0(3) 2.707 (2) Mo(l)-M0(2)’ Mo(l)-M0(3)’ 2.714 (2) M0(2)-M0(3) MO(2)-M0(3)’ 2.708 (2) Mo(l)-Se(l) Mo(l)-Se(Z) 2.575 (3) Mo(l)-Se(3) Mo(l)-Se(4) 2.573 (3) Mo(2)-Se(2) Mo(2)-Se(4) 2.563 (3) Mo(3)-Se(l) Mo(3)-Se(4) 2.570 (3) Mo(2)’-Se(1) Mo(2)’-Se(3) 2.571 (3) Mo(3)’-Se(2) Mo(3)’-Se(3) 2.580 (3) Mo(l)-P(l) Mo(2)-P(2) 2.578 (6) Mo(3)-P(3)

M0(2)-Mo(l )-Mo(3) Mo(Z)-Mo(l)-Se(l) Mo(l)-Se(l)-Mo(2)’

60.26 (6) 118.68 (9) 64.06 (7)

3.847 (3) 2.712 (3) 2.722 (3) 2.720 (2) 2.561 (3) 2.566 (3) 2.566 (3) 2.574 (3) 2.571 (3) 2.572 (3) 2.573 (6) 2.559 (6)

Mo(3)-Mo( l)-M0(3)’ Mo(2)’-Mo(l)-Se(l) Mo(2)-Mo(l)-P(I)

89.88 (7) 58.16 (7) 134.3 ( I )

“Prime indicates an atom with the equivalent position coordinates --x

‘12.

-y

+ ‘ 1 2 , -2.

8

-1.0

I

-1.5

I

-2.0

-2.5

2.698-2.862 2.684-2.836 2.706-2.804 2.701-2.776

(2.780) (2.760) (2.755) (2.738)

2.43-2.46 2.55-2.59 2.43-2.48 2.55-2.61

(2.44) (2.57) (2.45) (2.58)

3b 3b 3b 3b

could also be observed at lower potential (Table XII). Figure 4 shows a typical cyclic voltammogram of 1 in THF. The thin-layer coulometry of 1.2 mM solutions of 1 (ferrocene used as reference) indicated that each step was a one-electron redox process. The oxidation potentials for 1 and 2 in T H F are 0.16 and 0.19 V more positive, respectively, as compared with the values in dichloromethane. The reason for the solvent effect is not clear. The scan rates were varied from 20 to 200 mV s-l. The ipa/iF values of the T H F solutions were 1.0-1.1 for the first oxidation and reduction steps, but the ratio for the second reduction step was 0.71-0.73. These data imply the one-electron quasireversible redox processesI2 that are described as follows.

X = S, Se

90.00 (4) 57.14 (7) 133.39 (8)

“Prime indicates an atom with equivalent position coordinates -x -y

, -0.5

Table X. Bond Distances (A) in Complexes 1-4 and Chevrel Phases Mo-Mo: Mo-S: range (av) range (av) ref 2.662-2.664 (2.663) 2.44-2.45 (2.45) this work 2.697-2.708 (2.703) 2.55-2.57 (2.56) this work 2.664-2.677 (2.670) 2.44-2.47 (2.46) this work 2.707-2.722 (2.714) 2.56-2.58 (2.57) this work

89.98 (4) M0(3b)-Mo(Ib)-M0(3b)’

Prime indicates an atom with equivalent position coordinates -x, -y,

0

E vs SCE 1 v

59.86 (4)

Mo(lb)-Mo(Zb)-Se(3b) Mo(3b)-Mo(2b)-Se(3b) Mo(Zb)’-Se(lb)-Mo(3b)‘ Mo(Zb)-Mo(lb)-P(lb)

0.5

1-/2-

Figure 4. Cyclic voltammogram of [ M O ~ S , ( P E ~(1) ~ )in ~ ]THF.

60.07 (3) Mo(Zb)-Mo(lb)-M0(3b)

118.14 (5) 58.20 (4) 63.65 (4) 136.34 (9)

0/1-

+

solutions. In dichloromethane, an oxidation and a reduction process were observed, whereas in T H F another reduction process

Discussion Synthesis. Rational synthesis of cluster complexes is one of the most important fields in metal cluster ~hemistry.’~It is generally expected that use of building blocks to construct cluster skeletons offers more selective preparations than starting from mononuclear c~mplexes.’~Bridging chalcogen atoms are especially useful to bind building blocks.’5 Although the idea itself is not new, the number of successful examples has been limited. Recently, novel hexanuclear complexes have been prepared from trinuclear’6 and dinuclear c0mp1exes.l~ Some octahedral cluster compounds have been prepared from trinuclear c l ~ s t e r s . l ~The *’~ (12) (a) Zanello, P. Coord. Chem. Rev. 1988, 83, 199. (b) Lemoine, P. Coord. Chem. Reti. 1988,83, 169. (13) (a) Vargas, M. D.; Nicholls, J. N. Adti. Inorg. Chem. Radiochem. 1986, 30, 123. (b) Roberts, D. A.; Geoffroy, G. L. Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A,; Abel, E. W., Eds.; Pergamon: Oxford, England, 1982; Chapter 40. (14) Geoffroy, G. L. Metal Clusters in Catalysis; Gates, B. C., Guczi, L., Knozinger, H., Eds.; Elsevier: Amsterdam, 1986; Chapter I . (15) (a) Adams, R. D. Polyhedron 1985, 4, 2003. (b) Vahrenkamp, H. Angew. Chem., Int. Ed. Engl. 1975, 14, 322. (16) Adams, R. D.; Babin, J. E. Inorg. Chem. 1987, 26, 980. (17) Cotton, F. A.; Kibala, P. A.; Roth, W. J. J . Am. Chem. SOC.1988, 110, 298. (18) Johnson, B. F. G.; Johnston, R. D.; Lewis, J. J . Chem. SOC.A 1968, 2865. (19) (a) Perrin, C.; Sergent, M. New J . Chem. 1988, 12, 337. (b) Nanjundaswamy, K. S.;Vasanthacharya, N. Y.; Gopalakrishnan, J.; Rao, C. N. R. Inorg. Chem. 1987, 26, 4286.

Inorganic Chemistry, Vola29, No. 4, 1990 769

Models of the Superconducting Chevrel Phases

130.6

49 1

8.1 x 103 [Mo6Se8(PEt3)61

227.8 230.8

130.6

53.8

566

5.5 x 103

99 1 1.2 x 103 1034 1.4 x 103

1200 sh 1152 sh

“ C Is: 284.6 eV. bSolvent: 1, benzene: 2, chloroform.

Table XII. Formal Potentials for Complexes [MO&(PEt3)6] (1) and

IMo,Se8(PEt,),l (2)” Eo/V vs F,/F,+

solvent +1/0 -0.23 CHIC12 THF -0.07 -0.23 [ M0&8(PEt3),] CH2CI2 -0.05 THF “E0(F,/Fct) = 0.498 V (in CH,C12) and NaSCE. [ MO&(PEt3)6]

0/-1

-I/-2

-1.50 -1.50

-2.51

-1 S O -1.47

-2.45

0.595 V (in THF) vs

attempts to prepare molecular model compounds for the Chevrel phases by exchanging the face-bridging halides by chalcogenides have been partially rewarded.20 The designed synthesis of octahedral Chevrel models by condensation of two triangular cluster units in the present study provides the first example of such synthesis, and this method has successfully been applied to the synthesis of tungsten analogues.2’ Structure. Since the molybdenum cluster complexes studied in this work have no intercluster Mo-X bond as found in the solid-state Chevrel phases, the Mo-Mo bond distances should purely reflect the electronic factors of the molybdenum cluster and the effects of the chalcogen atoms. The Pauling bond order sum per electron PBO/e22values (eq 2) for complexes 1-4 are ~(Mo-Mo) = 2.619 - 0.60 log n PBO/e = 4 X n/(20/6) for 1 and 2; 4 X n/(21/6) for 3 and 4 (2) 1.07, 0.87, 0.93, and 0.79, respectively. These values are comparable with those for a number of hexanuclear clusters23and indicate that the Mo-Mo distances are predominated by the number of the bonding electrons on the molybdenum atoms. The results of the structure determinations show that the metal octahedra of the neutral complexes 1 and 2 are very regular, in contrast to the corresponding solid-state compounds Mo6X8(X = S, Se, Te) that contain trigonally elongated Mo, octahedra. It is not unreasonable that no distortion is observed in the neutral complexes because the triply degenerate HOMO2vZ4is completely occupied in these 20-electron clusters. The one-electron reduction of the neutral complex is accompanied by a slight elongation of the avera e metal-metal bond distance (0.1 1 ( 1 ) A in 3 and 0.010 (1) in 4), and a small distortion of the metal octahedron is found in the anionic complexes 3 and 4. Because the changes are very small, the nature of the LUMO where the additional electron enters is nonbonding or slightly antibonding with respect to the metal-metal bonding.

1

(a) Michel, J. B.: McCarley, R. E. Inorg. Chem. 1982, 21, 1864. (b) Ebihara, M.; Toriumi, K.; Saito, K. Inorg. Chem. 1988, 27, 13. Saito, T.; Yoshikawa, A.; Yamagata, T.; Imoto, H.; Unoura, K . Inorg. Chem. 1989, 28, 3588. Pauling, L. The Nature o j t h e Chemicul Bond, 3rd ed.; Cornell University, Press: Ithaca, NY, 1960; p 400. Corbett, J. D. J . Solid State Chem. 1981, 37, 335. (a) Le Beuze, L.; Makhyoun, M . A.; Lissillour, R.; Chermette, H. J . Chem. Phys. 1982,76,6060. (b) Hughbanks, T.; Hoffmann, R. J . Am. Chem. SOC.1983, 105, 1150. (c) Burdett, J. K.; Lin, J.-H. Inorg. Chem. 1982, 21, 5 . (d) Bullett, D. W. Phys. Reu. Lett. 1977, 39, 664. (e) Mattheiss, L. F.; Fong, C. Y. Phys. Reu. B. 1977, IS, 1760. (f) Bronger, W.; Miessen, H.-J. J . Less-Common Met. 1982, 83, 29.

The small distortion of the metal octahedron may be explained in terms of Jahn-Teller effect for the partial occupation of the egorbital. Especially in the sulfido complex 3, the main component of the distortion of the metal octahedron is the tetragonal elongation along the Mo(2)-Mo(2)’ axis: the distance Mo(2)-Mo(2)’ is longer than the other two metal-metal distances across the centers by 0.019 (2) A (Table VIII). The reduced complexes have molybdenum-chalcogen and molybdenum-phosphorus bond distances longer by 0.01-0.02 %, than those of the corresponding neutral complexes. These elongations can be attributed to the increase of the radius of the molybdenum due to the reduction. The elongation of the Mo-X bond distances on reduction is consistent with the result of the electronic structure calculation that the LUMO eg orbital has Mo-X antibonding The Mo-Mo distances in the selenido complexes, 2 and 4, are longer by 0.04 A than those in the corresponding sulfido complexes, 1 and 3. This elongation is associated with the larger van der Waals radius of selenium atom. Because the selenido ligands cannot approach each other as closely as sulfido ligands, they draw out the molybdenum atoms to which they are bonded. Similar effects have been observed in other chalcogenide and halide cluster compounds and have been termed as “matrix effects”.23 As discussed above, the structures of the molecular chalcogenide cluster complexes are quite normal; Le., the calculated PBO/e values are approximately equal to unity, the metal octahedral are regular for 20 electrons, and the replacement of sulfido ligands with selenido makes the metal-metal bond distances longer. In contrast, in the solid-state compounds, Mo,Xs and Chevrel phases M,Mo6Xs, PBO/e values are much lower than unity, the clusters show trigonally elongated octahedra, and the selenides have shorter metal-metal bond distances than the sulfides. Yvon proposed that the trigonal elongation and the shorter bond distance of the selenides could be associated with the effective number of electrons in the metal c l ~ s t e r .However, ~ Corbett argued that these are due to the intercluster metal-chalcogen interactions on the basis of the discussion of the PBO/e values of many cluster compounds! The present results clearly show that the number of electrons in the metal cluster alone cannot cause such structural features as found in the solid-state compounds because they are not observed in the molecular compounds with same number of electrons. On the other hand, the present results are completely consistent with Corbett’s conclusion that these anomalies of the solid-state compounds are due to the intercluster interactions. In addition, in the metal octahedra in the solid-state compounds M6X8with 20 electrons, the bands near the Fermi energy that corresponds to the HOMO and LUMO orbitals of the molecular complexes are not completely occupied due to the intercluster interaction. Such an electronic configuration may prefer the trigonal elongation of the metal octahedron as discussed by Noh1 et al.25 The electronic effects in the solid-state compounds are often masked by strong intercluster interactions between the discrete cluster units. The structures of the molecular model compounds are necessary to estimate the contribution of the electronic effects to the structures of the solid-state cluster compounds with the same cluster units. This conclusion does not always ignore the importance of the electronic effects also in the solid-state M6 cluster compounds. If other conditions such as intercluster bonding or (25) Nohl, H.; Klose, W.; Andersen, 0. Reference 2a, p 165

770 Inorganic Chemistry, Vol. 29, No. 4, 1990

Saito et al. Electrochemistry. The potentials for the sulfido and selenido complexes are not very different, and the extent of charge transfer from face-bridging selenium atoms to the cluster core in 2 may be similar to that from sulfur in 1. This is in accord with the result of the XPS (vide supra) and contradicts the view that the net charge transfer from the selenium atoms is larger than that from the sulfur atoms in the solid-state Chevrel phase^.^ The cluster complexes 1 and 2 show redox chemistry similar to that of [M&(PEt3)6] (M = Fe, cO),29but the filling Of the LUMO in the 20-electron molybdenum cluster complexes is more difficult. The one-electron-reduced clusters 3 and 4 are extremely sensitive to oxidation, and the preparation of more reduced species would be formidable.

...............

'2

-

...... .......

.Ir2$2;2u

+

-'I

......

tl" tl,

-31g-13

4-+*-

.........{ e ,

-4

................... ....................... .......:: t*,

1-5

...............tl" .................... t 2 g

> aJ

P

.....................

; " ' ! I

'a3 u"

0

....................

Figure 5. Electronic energy levels of [Mo&(PH,),] near the Fermi energy calculated by the DV-Xa method." The contributions of each atomic orbital are indicated by different kinds of lines.

crystal packing allow, 24-electron clusters tend to show regular octahedral structures26 and 23-, 22-,*' and 2 1-electron clusters are distorted. Spectra. The cluster complexes 1-4 show characteristic absorptions near 1000 and 500 nm (Table XI). The DV-Xa M O calculation of [Mo6S8(PH3)6]by Imoto (Figure 5)" indicates that the HOMO of this 20-electron cluster complex is the t,, orbital and the LUMO is the eg orbital. The t2gand tzuorbitals have slightly lower energy than the tl, orbital. The M O calculations on [Mo6Sg]*-or [Mo6S81e show different level orders,19 but our model is most closely related to complex 1 and it would be justifiable to correlate the spectra to the model. It is likely that the absorptions in the 1000-nm region are assignable to the eg tl, transition. The energy gap in the calculation is 0.98 eV. The notably high molar extinction coefficients of the bands indicate that the transitions have a charge-transfer nature. This is consistent with the result of the calculation that the HOMO t,, orbital is made mainly of sulfur p orbitals, and the LUMO eg orbital, of molybdenum d orbitals (orbital contributions: tl,, Mo 4 d 25%, S 3p 59%, P 3p 3%; eg, Mo 4d 66%, S 3p 22%, P 3p 0%). On reduction, the bands shift to somewhat lower energy. The binding energies of the molybdenum and phosphorus atoms in the XPS of 1 and 2 are almost identical, and the oxidation states of the cluster cores seem comparable.28 +-

( 2 6 ) Bronger. W.:Fleishhauer, J.; Marzi, H.; Raabe, G.; Schleker, W.: Schuster. T. J . Solid Store Chem. 1987. 70. 29. (27) Stollmaier, F.; Simon, A . Inorg. Chem. '1985, 24, 168

Conclusion The results of the present study have demonstrated that the 20-electron molecular cluster complexes 1 and 2 have regular octahedral cores. This is due to the virtual lack of intercluster Mo-X interaction and the absence of Jahn-Teller type distortion in 1 and 2. The selenido derivative 2 has Mo-Mo and Mo-X bond distances longer than those of the sulfido derivative 1. A slight distortion of the octahedra occurs on one-electron reduction of the complexes, and the average Mo-Mo and Mo-X bond distances become longer. The standard redox potentials are very similar for 1 and 2. The data conform to the small difference of the electronegativities of sulfur and selenium,30 and the net charge transfer from the eight chalcogen atoms should be similar. The longer Mo-Mo and Mo-Se bond distances in 2 as compared with those in 1 can be explained by the longer bond radius of the selenium atom. Because there is no anomaly in the molecular model complexes, the anomalous structural features in the solid-state Chevrel phases, at least in the simplest ModXs (X = S, Se) compounds, can be interpreted in terms of the strong intercluster Mo-X bonding3' Acknowledgment. Support from the Ministry of Education, Science and Culture of Japan (Grant-in-Aid for Special Project Research No. 621 15007 and for General Research No. 63430010) and the Iwatani Naoji Foundation's Research Grant is gratefully acknowledged. We thank Nippon Chemical Co. Ltd. for the gift of triethylphosphine. Supplementary Material Available: A detailed list of X-ray data collection conditions (Table SI), thermal parameters of 1-4 (Tables SII-SV), atomic parameters of fixed hydrogen atoms of 1 (Table SVI), and complete bond distances and angles of 1-4 (Tables SVII-SX) (17 pages); listings of observed and calculated structure factors ( 5 1 pages). Ordering information is given on any current masthead page. (28) Yashonath, S.; Hegde, M. S.; Sarcde, P. R.; Rao, C. N. R.; Umarji, A. M.; Subba Rao, G. V. Solid State Commun. 1981, 37, 325. (29) (a) Cecconi, F.; Ghilardi, C. A.; Midollini, S.; Orlandini, A. J. Chem. Sac., Dalton Tram. 1987,831. (b) Agresti, A.; Bacci, M.; Cecconi, F.; Ghilardi, C. A.; Midollini, S. Inorg. Chem. 1985, 24,689. (c) Cecconi, F.; Ghilardi, C. A.; Midollini, S.;Orlandini, A.; Zanello, P. Polyhedron 1986, 5 , 2121. (30) (a) Sen, K. D., Jargensen, C. K., Eds. Elecrronegatiuity;Structure and Bonding, Vol. 66; Springer: Berlin, 1987. (b) Pearson, R. G.Inorg. Chem. 1988, 27, 734. (31) Note added in proof Recently, Kubel and Yvon re rted that, in isoelectronic ternary phases MMo6S8 (M = YbZ+.E$, Sr2+,Ba2+, Ca2+),the Mo-Mo intracluster bonds correlate with matrix effect. See: Kubel, F.; Yvon, K . J . Solid State Chem. 1988, 73, 188.